Move variable quantification of variables not occurring in the head of a rule.

[Broes De Cat]

If a rule is quantified by variable x, but x occurs only in the body, should move x inside. At the moment, this happens in the parser, but the grounderfactory does not assume this as has some unnecessary code for it. Solution: make a transformation which does the moving and call it in both parser and grounderfactory.

[Bart Bogaerts]

This is done in pull request #24, as soon as it gets accepted, this issue should be marked as resolved

[Broes De Cat]

Resolved in pull request #24.